Turbosuperchargers with liquid-cooled bearing housings are employed to an increasing extent in turbosupercharged internal combustion engines to prevent coking of the oil in the bearing of the turbosupercharger. While the cooling liquid is circulated by a pump during operation of the engine, the liquid must be circulated by a suitable thermosiphon action or a follow-up electric pump after the internal combustion engine has been switched off so as to avoid temperature build-up due to retained heat in the turbosupercharger. However, the thermosiphon action to be obtained is often difficult due to unfavorable drops in temperature; electric follow-up liquid pumps require temperature-resistant materials, electric wiring and a switch relay and are thus very expensive.
From DE-OS No. 34 07 521 is known a liquid cooling system of the type mentioned, in which, in addition to the cooling circuit for the internal combustion engine, another cooling circuit is provided for the turbosupercharger. The inlet flow pipe of the turbosupercharger is connected to the outlet of a radiator attached to the cooling circuit for the internal combustion engine. The return flow pipe of the turbosupercharger flows into the inlet flow pipe of the internal combustion engine just before the circulating pump which is attached to the cooling circuit of the internal combustion engine. The inlet flow pipe of the turbosupercharger is connected via a branch pipe to a heat exchanger that is geodetically situated higher, and another branch pipe connects the return flow pipe of the turbosupercharger to the heat exchanger. An expansion tank for the temperature variable volume of cooling liquid is employed as the heat exchanger.
The expansion tank is filled up to a certain level, and the two branch pipes flow into the expansion tank below this level. A one-way or check valve is mounted in the branch pipe that connects the expansion tank to the return flow pipe of the turbosupercharger, which allows flow through this branch pipe only toward the expansion tank. In lieu of the check valve, a remote-controllable magnetic valve can also be installed in the branch pipe.
During operation of the internal combustion engine, cooling liquid flows through the first cooling circuit which is attached to the internal combustion engine as well as the second cooling circuit which is attached to the turbosupercharger. The check valve makes it impossible for the cooling liquid to flow from the expansion tank through the branch pipe which is attached to the return flow pipe of the turbosupercharger bypassing the turbosupercharger in its return flow pipe.
After the internal combustion engine has been shut off, and thus the circulating pump as well, a pressure equilibrium occurs in the entire cooling circuit of the internal combustion engine, whereby the forced circulation cooling is ended. The hot cooling liquid of the turbosupercharger can then rise up to the expansion tank through its return flow pipe and through the branch pipe that is attached to it. The cooling liquid cools off in the expansion tank and flows back through the inlet flow pipe to the turbosupercharger. Thus, after the internal combustion engine is shut off, the turbosupercharger is cooled exclusively through thermosiphon action with the disadvantage initially described.